New lens for my nikon d3100?

I want to buy a new lens to go with my kit lens, but I can't decide what! I love taking pictures of people mostly. A nice DOF would be nice too, so that I can isolate the subject/person. Also since I spent all my money on the d3100, I can't afford a really expensive lens. Any suggestions?

Cheapest you can get is a 50mm f1.8. However, that will not autofocus on the camera. Alternative is to save a bit more and go for the 60mm f2.8 macro lens.

First learn how to use your fine camera using the 18-55 mm lens.

If you use the existing lens at 55 mm with the aperture wide open and the subject close to your lens, you can use selective focus.

There are four lens uses you can consider and start saving for them as you lean how to use your camera.

Landscapes: AF-S 10-24 mm, $900
Macro: AF-S 60 mm f/2.8, $600 or AF-S 85 mm f/3.5, $530
Action and wildlife: AF-S 55-300 mm, $400
Portrait: AF-S 50 mm f/1.4, $485

I agree with fhotoace, you have plenty of challenge with the kit lens. If you absolutely have to buy another lens at this time, and I understand that need, I suggest the Nikkor 35mm f/1.8 lens for about $225 or the Nikkor 50mm f/1.8 lens for about $125. What they allow you to do is to take pix in a lot less light.
http://www.amazon.com/...zon.com/s/

50mm f1.8. A must have for everyone. Amazing DOF. $135. Get it.